The use of the Optical Coherence Tomography (OCT) has increased markedly over the recent years for clinical research. It is a promising new method for imaging the retina, measuring its thickness, and displaying some features of its structure. It is useful in assessing several eye diseases, including macular edema from various causes and abnormalities of the vitreoretinal interface. There is a broad clinical consensus that OCT is superior to stereoscopic color fundus photography, fluorescein angiography, and clinical biomicroscopic examination in measuring retinal thickness and is capable of documenting fairly small changes in thickness. OCT is becoming an important part of clinical trials of new treatments for macular edema. A number of models of the OCT device are commercially available, models 1, 2, and 3. A number of models of OCT have been used in clinical centers involved in such clinical research. Comparisons of these models 2 and 3 as well as the reproducibility of these measurements have not been conducted. The main research questions to be answered in this protocol are the following, in patients with normal retina, diabetic macular edema, macular edema from other causes, or other vitreoretinal abnormalities: 1. Is the standard deviation of the differences of sequential measurements of retinal thickness in normal retinas using OCT 3 similar to those measured with the OCT 2? 2. Are there systematic differences between thickness measurements using OCT 2 and OCT 3 in the same eyes? 3. Are there differences in the ability of each machine to image abnormalities within the vitreoretinal interface?